the trac loc is what the clutch type, the power lock is the bolt together style? i have the clutch type and going 11.80 i think im pushing a little more than 300 hp. i pretty much beat the hell out of it and have never had a problem. the guy that built my dana did want to use the power lock but you cant get them new. and a detroit locker is over 500 i think. so i settled for this. he told me id be fine, and if i wanted it tighter i could just tighten up the clutch pack, but i like it. its a tuff unit, you can buy them new from strange and others for around 285 bucks. my bud also used a stock one and rebuilt it and added 35 spline side gears his car with a stick went low 12's and yanks both wheels, no problems yet. i could be thinking of the wrong unit though, i guess.
I love Fords, but their factory Trac-Loc unit is a piece of garbage. After 100,000 miles, they're toast. Do yourself a favor, and buy a Detroit Locker or a selectable locker ( OX, E-Locker, ARB ) if you're going racing or don't want to be the guy leaving one leggers all over town.